The nervous system is a complex, highly specialized network. It organizes, explains, and directs interactions between a subject and the subject's environment. For example, the nervous system controls: sight, hearing, taste, smell and feeling (sensation); voluntary and involuntary functions, such as movement, balance and coordination, as well as blood flow and blood pressure; and the ability to think and reason. The nervous system is divided into the brain and spinal cord (central nervous system) and the nerve cells that control voluntary and involuntary movements (peripheral nervous system or PNS). The PNS is further divided into the sensory-somatic nervous system and the autonomic nervous system (ANS). The ANS regulates the intrinsic function and balance of each body organ, and is always functioning to maintain homeostasis and balance of each organ. Persistent imbalance of the ANS, however, can adversely influence body organ function.